The overall objective of the proposed research is to understand the role of population structure in the evolution of a species. Population structure is the way in which breeding individuals are distributed within and among demes and their pattern of movement among demes. Population subdivision has both ecological and genetic consequences. The genetic effects of random genetic drift can result in the genetic differentiation of an array of local demes. The rate and degree of genetic differentiation depend on the numbers of locally breeding adults and the amount and pattern of dispersion among locals demes. the ecological effects of subdivision influence the process of selection within and among demes. The ecological and genetic effects interact to determine the relative importance of intra and interdemic selection to the overall evolution of the species. We are combining experimental studies, using laboratory populations of flour beetles (genus Tribolium), with theoretical models of the relevant genetic phenomena to investigate those kinds of population structures that are likely to have important evolutionary consequences for a species. Evolution is structured population is the central feature of Wright's Shifting Balance Theory of Evolution, one of the most comprehensive theories of genetics and evolution. The proposed research will provide an experimental foundation for Wright's theory with special emphasis on the role of gene interactions in the "interdemic-phase" of adaptive evolution.